Means "Japanese Domestic Market". Bought some for my Corolla, they had holes for "city lights". Over in Japan the island is so crowded and so lit they don't need full headlights all the time at night, so they put little bulbs in the housings too, run just them a lot of the time.

The holes have to be plugged so moisture doesn't get in there and condense. I put LEDs in them, wired to a simple toggle switch circuit. Looked pretty nifty really.

Some of the real JDM housings don't have DOT approval molded into them and a sharp car inspection place will catch that and fail you.